Blue luminescent zinc(II) complexes with polypyridylamine ligands: Crystal structures and luminescence properties

Article abstract of DOI:10.1039/a900504h

A series of blue luminescent zinc(II) complexes, [Zn(dpa)X₂] [dpa = di-2-pyridylamine, X = OAc 1a, Cl 1b, CN 1c or 4-MeC₆H₄S 1d], [Zn(dpa)₂][CF₃SO₃]₂ 2, [Zn(tpda)X₂] [tpda = 2,6-bis(2-pyridylamino)pyridine, X = OAc 3a or Cl 3b] and [Zn(tpda)(CF₃SO₃)₂] 4 has been prepared. Their molecular structures, except complex 4, have been established by X-ray crystallography. In the crystal lattice of 2 the [Zn(dpa)₂]²⁺ cations and CF₃SO₃^- anions are disposed in pairs via intermolecular hydrogen bonds [N(2)...O(2) 2.865(4) A]. The crystal packing of [Zn(dpa)(OAc)₂] 1a revealed that two adjacent molecules associate in pairs through intermolecular hydrogen bonding [N(2) ...O(4′) 2.816(3) A]. However, the crystal lattice of its tpda derivative 3a shows that the molecules are linked by extensive intermolecular hydrogen bonding between the amino groups and the acetate ligands [N(2)...O(2′) 2.805(3) and N(4)...O(4′) 2.860(3) A] resulting in an interlocking hydrogen bond network. Polymeric one-dimensional tapes are generated through extended π-π stacking interactions between the molecules of [Zn(dpa)(4-MeC₆H₄S)₂] 1d, and the thiolate groups are aligned in an all-anti conformation along the metal chain. In the case of [Zn(dpa)(CN)₂] 1c, co-operative intermolecular hydrogen bonds and aromatic π-π interactions in its solid state lead to a supramolecular two-dimensional sheet. All the zinc(II) complexes display high energy intraligand ¹(π-π*) fluorescence in degassed MeOH at 298 K, and intraligand ³(π-π*) phosphorescence in a glassy solution (MeOH-EtOH 1:2 at 77 K). An emission band observed for 1c (418 nm) and 1d (481 nm) in their solid state emission spectra is ascribed to excimeric emission due to aromatic π-π interactions.

Full text of DOI:10.1039/a900504h

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Blue luminescent zinc(II) complexes with polypyridylamine ligands:
crystal structures and luminescence properties
Kin-Ying Ho, Wing-Yiu Yu, Kung-Kai Cheung and Chi-Ming Che*
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Received 19th January 1999, Accepted 16th March 1999
A series of blue luminescent zinc() complexes, [Zn(dpa)X2] [dpa = di-2-pyridylamine, X = OAc 1a, Cl 1b, CN 1c or
4-MeC6H4S 1d], [Zn(dpa)2][CF3SO3]2 2, [Zn(tpda)X2] [tpda = 2,6-bis(2-pyridylamino)pyridine, X = OAc 3a or Cl 3b]
and [Zn(tpda)(CF3SO3)2] 4 has been prepared. Their molecular structures, except complex 4, have been established by
X-ray crystallography. In the crystal lattice of 2 the [Zn(dpa)2]2ϩ cations and CF3SO3Ϫ anions are disposed in pairs via
intermolecular hydrogen bonds [N(2) ؒ ؒ ؒ O(2) 2.865(4) Å]. The crystal packing of [Zn(dpa)(OAc)2] 1a revealed that
two adjacent molecules associate in pairs through intermolecular hydrogen bonding [N(2) ؒ ؒ ؒ O(4Ј) 2.816(3) Å].
However, the crystal lattice of its tpda derivative 3a shows that the molecules are linked by extensive intermolecular
hydrogen bonding between the amino groups and the acetate ligands [N(2) ؒ ؒ ؒ O(2Ј) 2.805(3) and N(4) ؒ ؒ ؒ O(4Ј)
2.860(3) Å] resulting in an interlocking hydrogen bond network. Polymeric one-dimensional tapes are generated
through extended π–π stacking interactions between the molecules of [Zn(dpa)(4-MeC6H4S)2] 1d, and the thiolate
groups are aligned in an all-anti conformation along the metal chain. In the case of [Zn(dpa)(CN)2] 1c, co-operative
intermolecular hydrogen bonds and aromatic π–π interactions in its solid state lead to a supramolecular two-
dimensional sheet. All the zinc() complexes display high energy intraligand 1(π–π*) fluorescence in degassed MeOH
at 298 K, and intraligand 3(π–π*) phosphorescence in a glassy solution (MeOH–EtOH 1:2 at 77 K). An emission
band observed for 1c (418 nm) and 1d (481 nm) in their solid state emission spectra is ascribed to excimeric emission
due to aromatic π–π interactions.
Introduction
Experimental
The search for blue luminous materials for applications in blue
light-emitting devices (LEDs) remains an ongoing interest
in materials sciences.1–5 The first realization of blue electro-
luminescence using poly(9,9-dihexylfluorene)4a,b and poly(para-
phenylene)4c had triggered an intensive research in this area.4d
Thus far, the studies have mainly been focused on the use
of aromatic organic molecules or conjugated organic polymers
as the light emitting materials.1 Blue luminescent inorganic
and organometallic compounds have limited precedents;3,5
a notable example is the [Zn4O(AID)6] (AID = 7-Azaindolate)
complex which has successfully been applied to the construc-
tion of a blue LED device.5a,b Prompted by the recent reports on
blue photoluminescence from organoaluminum() complexes6
of di-2-pyridylamine and the formation of an intermolecular
hydrogen bonded metal chain in its cobalt derivative,7 the use of
this and related ligands as structural motifs have received our
attention for developing new blue luminous materials with a
polymeric supramolecular structure.8 Self-assembly of molecu-
lar components based on hydrogen bonding and aromatic π–π
stacking interactions has been widely investigated, and these
intermolecular forces are readily harnessed to provide an effect-
ive approach to generate a diversity of superstructures from
properly designed structural elements.9
All the starting materials were used as received and solvents
purified according to the literature methods.10 Di-2-pyridyl-
amine was obtained commercially, whereas 2,6-bis(2-pyridyl-
amino)pyridine was prepared by the coupling reaction between
2,6-diaminopyridine and 2-bromopyridine.8b The UV-vis
spectra were recorded on a Perkin-Elmer Lambda 19 spectro-
photometer, emission spectra on a SPEX Fluorolog-2 Model
F11 fluorescence spectrophotometer. Emission lifetimes of
the zinc complexes were measured with a Quanta Ray DCR-3
Nd-YAG laser as the excitation light source (pulse output 266
nm, 8 ns). The 1H NMR spectra were recorded on a DPX-300
Bruker FT spectrometer with chemical shifts (in ppm) relative
to tetramethylsilane. Elemental analyses were performed by
Butterworth Laboratories Ltd., Teddington, UK.
Preparation of 2,6-bis(2-pyridylamino)pyridine
A solution of 2,6-diaminopyridine (2.50 g, 22.9 mmol) in
THF (30 cm3) was added to a suspension of NaH (50%, 3.30 g,
68.7 mmol) in THF (30 cm3). After stirring for 30 min,
2-bromopyridine (8.7 cm3, 91.6 mmol) was added to give a
greenish grey suspension, which was refluxed for 24 h resulting
in a brown solution. After solvent evaporation, the residue
was washed successively with brine solution (15 cm3) and
diethyl ether (15 cm3). The product solid was collected on a
We herein describe a full account on the preparation and
structural characterization of a series of zinc() complexes
containing di-2-pyridylamine (dpa) and 2,6-bis(2-pyridyl-
amino)pyridine (tpda) ligands, which were found to exhibit blue
photoluminescence. In general, these complexes show self-
assembled supramolecular structures in the solid state via
co-operative hydrogen bonds and/or aromatic π–π interactions
to generate pairs, chains or networks. Part of this work has been
reported in a communication.5c
1
frit and air-dried. Yield: 3.50 g, 58%. H NMR (270 MHz,
dmso-d6): δ 9.37 (2 H, s, NH), 8.21 (2 H, dd, 4J = 1.3, 3J = 4.9),
3
4
3
7.84 (2 H, d, J = 8.4), 7.64 (2 H, dt, J = 1.9, J = 7.8), 7.51
3
3
(1 H, t, J = 8.0), 7.14 (2 H, d, J = 8.0) and 6.87 (2 H, dt,
4J = 0.6 Hz, J = 8.0 Hz). EI-MS: m/z 270 [Mϩ]. The spectral
3
characterization data are comparable to reported values, see
ref. 8(b).
J. Chem. Soc., Dalton Trans., 1999, 1581–1586
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Metal complex preparation
81% (Found: C, 51.08; H, 4.25; N, 15.61. Calc. for
1
C19H19N5O4Zn: C, 51.09; H, 4.29; N, 15.67%). H NMR (270
[Zn(dpa)(OAc)2] 1a. A methanolic solution (20 cm3) of
dpa (0.17g, 1 mmol) was added to a refluxing solution of
Zn(OAc)2ؒ2H2O (0.22 g, 1 mmol) in MeOH (30 cm3). The color-
less solution was refluxed for 5 h. After cooling to room
temperature, the solvent was removed by rotary evaporation
and the white residue recrystallized by slow diffusion of diethyl
ether into a methanolic solution to afford colorless crystals:
yield 0.30 g, 85% (Found: C, 47.25; H, 4.21; N, 11.92. Calc. for
C14H15N3O4Zn: C, 47.41; H, 4.26; N, 11.85%). δH (270 MHz;
MHz, CD3OD): δ 8.60 (d, 2 H, 3J = 4.8), 8.02 (t, 2 H, 3J = 7.2),
3
7.87 (t, 2 H, J = 7.9), 7.28 (m, 4 H), 7.00 (m, 1 H) and 6.82
(d, 2 H, 3J = 8.1 Hz). FAB-MS: m/z 386 [Mϩ Ϫ OAc].
[Zn(tpda)Cl2] 3b. A similar procedure as for complex 1b
was employed, except that tpda was used. Yield: 0.30 g, 75%
(Found: C, 45.20; H, 3.19; N, 17.50. Calc. for C15H13Cl2N5Zn:
1
C, 45.09; H, 3.28; N, 17.53%). H NMR (270 MHz, dmso-d6):
δ 9.59 (s, 2 H), 8.32 (m, 2 H), 7.73 (m, 5 H) and 6.97 (m, 4 H).
4
3
CD3OD) 8.38 (2 H, dd, JHH = 1.2, JHH = 5.6, aryl H), 7.93
FAB-MS: m/z 362 [Mϩ Ϫ Cl].
(2 H, td, 4JHH = 1.9, 3JHH = 7.9, aryl H), 7.20 (2 H, d, 3JHH = 8.6,
4
3
aryl H), 7.16 (2 H, td, JHH = 1.0, JHH = 6.5 Hz, aryl H) and
1.98 (6 H, s, CH3). FAB-MS: m/z 294 [Mϩ Ϫ OAc].
[Zn(tpda)(CF3SO3)2] 4. A similar procedure as for complex
1e was employed. Yield: 0.41 g, 66% (Found: C, 32.31; H, 2.22;
N, 11.25. Calc. for C17H13F6N5O6S2Zn: C, 32.58; H, 2.09;
[Zn(dpa)Cl2] 1b. The procedure was similar to that for
complex 1a except ZnCl2 was used and hot DMF for re-
crystallization: yield 0.25 g, 80% (Found: C, 38.93; H, 2.99;
N, 13.75. Calc. for C10H9Cl2N3Zn: C, 39.06; H, 2.95; N,
13.67%). δH (270 MHz; DMSO-d6) 8.20 (2 H, d, 3JHH = 2.6, aryl
1
N, 11.17%). H NMR (270 MHz, CD3OD): δ 7.91 (m, 1 H),
7.77 (m, 4 H) and 6.89 (m, 6 H). FAB-MS: m/z 476 [Mϩ Ϫ
CF3SO3].
3
Crystal structure determinations
H), 7.80 (2 H, m, aryl H), 7.58 (2 H, d, JHH = 8.4, aryl H)
3
and 7.01 (2 H, t, JHH = 6.3 Hz, aryl H). FAB-MS: m/z 270
For complex 3b, a Rigaku AFC7R diffractometer with
graphite-monochromatized Mo-Kα radiation (λ = 0.71073 Å)
was employed. The structure was solved by Patterson methods
and expanded by Fourier methods (PATTY).11 The structure
was refined by full-matrix least squares using the software
package TEXSAN12 on a Silicon Graphics Indy computer. One
crystallographic asymmetric unit contains one formula unit.
In the least-squares refinement, 13 non-H atoms were refined
anisotropically, the positional parameters of H(1) bonded to
N(2) located in a Fourier-difference synthesis were refined,
and the H atoms at the calculated positions with thermal
parameters equal to 1.3 times that of the attached C atoms were
not refined.
[Mϩ Ϫ Cl].
[Zn(dpa)(CN)2] 1c. A methanolic solution (20 cm3) of dpa
(0.17 g, 1 mmol) was added to a refluxing suspension of
Zn(CN)2 (0.12 g, 1 mmol) in MeOH (30 mL). The mixture was
refluxed overnight, and the white solid collected by filtration
after cooling to room temperature. The product complex was
extracted from the white solid into boiling methanol, and pale
yellow crystals (yield 0.17 g, 60%) were obtained on cooling
of the hot methanolic extract (Found: C, 49.99; H, 3.02;
N, 24.41. Calc. for C12H9N5Zn: C, 49.94; H, 3.14; N, 24.27%).
FT-Raman: 2164, 2153, 1619, 1587 and 1436 cmϪ1. δH (270
MHz; CD3OD) 10.11 (1 H, s, NH), 8.20 (2 H, d, 3JHH = 4.3, aryl
H), 7.81 (2 H, t, 3JHH = 7.3, aryl H), 7.56 (2 H, d, 3JHH = 7.2, aryl
For complexes 1a, 1b, 1d, 2 and 3a, a MAR diffractometer
with graphite-monochromatized Mo-Kα radiation (λ = 0.71073
Å) was employed. The structure for 2 was solved by direct
methods (SIR 92)13 and the Patterson method was used for the
others. The structures were expanded by Fourier methods
(PATTY)11 and refined by full-matrix least squares using the
software package TEXSAN12 on a Silicon Graphics Indy
computer. For 2, one crystallographic asymmetric unit con-
tains half of the complex cation with the Zn atom at a special
3
H) and 7.02 (2 H, t, JHH = 6.0 Hz, aryl H). FAB-MS: m/z 289
[M]ϩ and 261 [Mϩ Ϫ CN].
[Zn(dpa)(4-MeC6H4S)2] 1d. To a hot methanolic solution (20
cm3) of zinc acetate (0.22 g, 1 mmol) was added 4-methyl-
benzenethiol (0.26 g, 2 mmol) in MeOH (10 cm3); the colorless
mixture was refluxed for 15 min followed by addition of dpa
(0.17 g, 1 mmol) in MeOH (10 cm3). The reaction mixture was
refluxed for 15 min. After the solution was cooled to room
temperature, solvent was removed by rotary evaporation. The
solid residue was recrystallized in MeOH–Et2O to afford a
colorless crystalline solid. Yield: 0.43 g, 90% (Found: C, 59.36;
H, 5.01; N, 8.54. Calc. for C24H23N3S2Zn: C, 59.68; H, 4.80;
N, 8.70%). 1H NMR (270 MHz; dmso-d6) δ 8.19 (d, 2 H,
3J = 4.7), 7.74 (m, 2 H), 7.50 (s, 1 H), 7.07 (m, 4 H), 6.97 (m,
Ϫ
position plus one CF3SO3 anion. For other complexes, one
crystallographic asymmetric unit consists of one molecule. In
the least-squares refinement all the non-H atoms were refined
anisotropically; the H atoms bonded to the amino groups were
located in the Fourier-difference synthesis and their positional
parameters refined. The other H atoms at the calculated
positions with their thermal parameters equal to 1.3 times those
of the attached C atoms were not refined.
CCDC reference number 186/1387.
See http://www.rsc.org/suppdata/dt/1999/1581/ for crystallo-
graphic files in .cif format.
3
2 H), 6.76 (d, 4 H, J = 7.1 Hz) and 2.13 (s, 6 H). FAB-MS:
m/z 358 [Mϩ Ϫ SC7H7].
[Zn(dpa)2][CF3SO3]2 2. A mixture of complex 1b (0.31 g,
1 mmol) and Ag(CF3SO3) (0.57 g, 2.2 mmol) in MeOH (50 cm3)
was refluxed for 2 h. After cooling to room temperature the
colorless solution was filtered through Celite and the filtrate
was evaporated to dryness. The white residue was recrystallized
in MeOH–Et2O to afford colorless crystals. Yield: 0.29 g,
41% (Found: C, 37.02; H, 2.84; N, 11.84. Calc. for C22H18-
Results and discussion
2,6-Bis(2-pyridylamino)pyridine was previously synthesized
by Peng and co-workers8b using the coupling reaction of 2-
bromopyridine and 2,6-diaminopyridine with tBuOK as a base
in THF (26% yield). In this work, we employed NaH for the
coupling reaction, and a much better product yield of 58%
was obtained (Scheme 1). The treatment of Zn(OAc)2ؒ2H2O,
ZnCl2 and Zn(CN)2 with the ligands dpa or tpda in methanol
afforded monomeric zinc() complexes in high yields. The tri-
flatozinc() derivatives were prepared by metathesis of the
chlorozinc() complexes with silver() triflate. All the complexes
reported, except [Zn(tpda)(CF3SO3)2] 4, had their molecular
structures determined by X-ray crystallography. The structure
1
F6N6O6S2Zn: C, 37.43; H, 2.57; N, 11.91%). H NMR (270
3
MHz, CD3OD): δ 10.12 (s, 1 H), 8.20 (d, 2 H, J = 4.9), 7.81
(t, 2 H, 3J = 7.2), 7.56 (d, 2 H, 3J = 8.2) and 7.03 (t, 2 H,
3J = 5.8 Hz). FAB-MS: m/z 555 [Mϩ Ϫ CF3SO3] and 384
[Mϩ Ϫ CF3SO3 Ϫ dpa].
[Zn(tpda)(OAc)2] 3a. A similar procedure was employed
as for complex 1a, except that tpda was used. Yield: 0.36 g,
1582
J. Chem. Soc., Dalton Trans., 1999, 1581–1586

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NaH
HN
N
NH
H2N
N
NH2
Br
THF, reflux
N
N
N
tpda
Scheme 1
Fig. 3 Perspective view of [Zn(tpda)(OAc)2] 3a. Details as in Fig. 1.
Fig. 1 Perspective view of [Zn(dpa)2][CF3SO3]2 2 (50% thermal ellips-
oids) and atom-numbering scheme.
Fig. 4 The crystal packing diagram of [Zn(dpa)2][CF3SO3]2 2. Each
[Zn(dpa)2]2ϩ cation associates with one molecule of CF3SO3 anion
Ϫ
through intermolecular hydrogen bonding [N(2)H ؒ ؒ ؒ O] resulting in
ion-pair formation.
The complexes 3a and 3b with tpda are isostructural (Fig. 3),
and the zinc atoms adopt a distorted trigonal bipyramidal
configuration. The N(1)–Zn–N(5) bond angle of 3a was found
to be 177.00(9)Њ [the corresponding bond angle for 3b =
176.98(9)Њ], while the N(1), Zn atoms and the two auxiliary
η1-OAc ligands are located on the equatorial plane. For all the
zinc complexes described in this work the Zn–N (pyridyl)
distances are in a 1.972(3)–2.129(2) Å range, comparable to the
corresponding distances [2.148(9) and 2.082(9) Å] found for
[Zn(L)(dien)](NO3)2 [dien = bis(2-aminoethyl)amine].14
Self-assembly of molecular components via intermolecular
hydrogen bonding and/or π–π stacking interactions has re-
ceived intense interest in crystal engineering.9 We found several
types of supramolecular structures such as molecular pairing,
polymeric tapes and networks in the crystal lattices of the
zinc() complexes of dpa and tpda ligands via these inter-
molecular interactions.
Fig. 2 Perspective view of [Zn(dpa)(OAc)2] 1a. Details as in Fig. 1.
of 1c has previously been communicated.5c The crystal data,
selected bond lengths and bond angles are in Tables 1 and 2
respectively.
Both dpa and tpda co-ordinate to ZnII via the pyridyl
nitrogen atoms. For dpa as the ligand, complexes 1b–1d and
2 are isostructural and the zinc atoms adopt a distorted
tetrahedral co-ordination geometry (Fig. 1). The zinc atom
of [Zn(dpa)(OAc)2] 1a is five-co-ordinated, and both η1 and η2
co-ordination modes are observed for the two acetate ligands.
The Zn–OAc distances are 1.960(2) Å for the η1-OAc, 2.166(2)
and 2.149(2) Å for the η2-OAc (Fig. 2). The N(1)–Zn–O(1) and
N(3)–Zn–O(2) angles are 145.5(1) and 141.0(1)Њ respectively,
whereas the respective O(3)–Zn–N(1) and O(1)–Zn–N(3) angles
are 111.72(9) and 95.36(9)Њ.
The crystal packing diagram of [Zn(dpa)2][CF3SO3]2
2
(Fig. 4) shows that each [Zn(dpa)2]2ϩ cation associates with one
Ϫ
CF3SO3 anion by hydrogen bonding interaction between the
unbound amino group and one of the oxygen atoms of the
adjacent triflate anion, resulting in ion pairings [N(2) ؒ ؒ ؒ O(2Ј)
2.865(4) Å]. However, no extended intermolecular hydrogen
bondings are recognized. Likewise, molecular pairing of the
J. Chem. Soc., Dalton Trans., 1999, 1581–1586
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neutral [Zn(dpa)(OAc)2] 1a via two intermolecular hydrogen
bonds between the non-co-ordinating N–H group and the
η1-acetate group of the adjacent molecule is evident. The
N(2) ؒ ؒ ؒ O(4Ј) distance is found to be 2.816(3) Å. As revealed by
the crystal packing of 1a shown in Fig. 5, the molecular pairs
are disposed in a herringbone-type pattern.15
In the case of [Zn(tpda)(OAc)2] 3a, there are two non-
co-ordinating amino groups [N(4)–H and N(2)–H] available for
hydrogen bonding for each tpda ligand. Its crystal packing
diagram (Fig. 6) shows that the molecules associate with
each other by extensive intermolecular hydrogen bonding
interactions between the N(4)–H group and the O(4Ј) atom of
the acetate group of an adjacent molecule [N(4) ؒ ؒ ؒ O(4Ј)
2.860(3) Å] in a head-to-tail fashion leading to an infinite
one-dimensional zigzag chain with an obvious directionality.
Each of the chains are cross-linked with neighbouring chains
by extensive hydrogen bonds between N(2)–H(1) ؒ ؒ ؒ O(2Ј) and
N(2Ј)–H(1Ј) ؒ ؒ ؒ O(2) atoms [N(2) ؒ ؒ ؒ O(2Ј) distance 2.805(3) Å]
along the chains creating a two-dimensional interlocking
hydrogen bonding network.
Fig. 7 depicts the crystal lattice packing of [Zn(dpa)-
(4-MeC6H4S)2] 1d. The glide-related molecules self-assemble
through aromatic π–π stacking interactions to form an infinite
one-dimensional tape with the interplanar distance between
the pyridyl rings being 3.5–3.7 Å. The thiolate moieties are
aligned in an anti conformation along the polymeric chain.
Fig.
5 Herringbone-type crystal packing of [Zn(dpa)(OAc)2] 1a
molecules. The molecular pairing is generated by two intermolecular
hydrogen bonds [N(2)H ؒ ؒ ؒ O(4)] between two complexes.
Fig. 6 The crystal packing diagram of [Zn(tpda)(OAc)2] 3a shows a
self-assembled 2-D network structure resulting from two types of
extended intermolecular hydrogen bonds [N(2)H ؒ ؒ ؒ O(2) (denoted as
a) and N(4)H ؒ ؒ ؒ O(4) (b)].
Fig. 7 The crystal packing diagram of [Zn(dpa)(4-MeC6H4S)2] 1d
shows a self-assembled infinite 1-D tape structure generated by exten-
sive aromatic π–π interactions.
Table 1 Crystallographic data for complexes 1a, 1b, 1d, 2, 3a and 3b
1a
1b
1d
2
3a
3b
Formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
C14H15N3O4Zn
354.67
Monoclinic
P21/c (no. 14)
10.310(2)
8.339(2)
17.935(3)
—
102.43(2)
—
1505.8(5)
4
C10H9Cl2N3Zn
307.49
C24H23N3S2Zn
482.97
C20H18N6Znؒ2CF3SO3
C19H19N5O4Zn
446.77
Monoclinic
P21/c (no. 14)
9.662(2)
8.016(2)
24.566(4)
—
92.16(2)
—
1901.3(6)
4
C15H13Cl2N5Zn
399.59
Monoclinic
C2/c (no. 15)
7.519(2)
17.202(2)
12.869(2)
—
103.96(1)
—
1615.4(5)
4
705.91
Monoclinic
C2/c (no. 15)
16.393(3)
8.897
19.610(3)
—
103.05(2)
—
2786.2(9)
4
Triclinic
Triclinic
¯
¯
P1 (no. 2)
P1 (no. 2)
7.439(2)
8.669(2)
9.409(2)
75.28(2)
89.32(2)
86.11(2)
585.5(2)
2
8.637(2)
11.018(2)
12.138(2)
86.55(2)
86.59(2)
80.74(2)
1136.5(4)
2
β/Њ
γ/Њ
V/Å3
Z
Rint
0.034
16.52
0.038
25.26
0.038
12.80
0.036
11.21
0.049
13.30
0.018
18.56
µ/cmϪ1
T/K
No. unique data
301
2929
301
2512
301
4950
301
2573
301
3749
301
1656
No. data with I > 3σ(I)
R
2326
0.036
2291
0.049
4108
0.042
2097
0.054
2791
0.040
1367
0.022
RЈ
0.056
0.066
0.064
0.082
0.054
0.030
1584
J. Chem. Soc., Dalton Trans., 1999, 1581–1586

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Table 2 Selected bond lengths (Å) and bond angles (Њ) for complexes
1a, 1b, 1d, 2, 3a and 3b
Table 3 The UV-vis spectral data for complexes 1–4 in MeOH at
298 K
Complex
λ/nm (ε/dm3 molϪ1 cmϪ1
)
Complex 1a
[Zn(dpa)(OAc)2]
[Zn(dpa)Cl2]
[Zn(dpa)(CN)2]
[Zn(dpa)(4-MeC6H4S)2]
[Zn(dpa)2][CF3SO3]2
[Zn(tpda)(OAc)2]
[Zn(tpda)Cl2]
257 (20000), 315 (18000)
255 (18000), 315 (17000)
257 (18000), 316 (16000)
256 (50000), 317 (16000)
Zn–N(1)
Zn–O(1)
Zn–O(3)
Zn–N(3)
Zn–O(2)
2.055(3)
2.166(2)
1.960(2)
2.039(2)
2.149(2)
N(1)–Zn–N(3)
N(1)–Zn–O(2)
N(3)–Zn–O(1)
N(3)–Zn–O(3)
O(1)–Zn–O(3)
N(1)–Zn–O(1)
N(1)–Zn–O(3)
N(3)–Zn–O(2)
O(1)–Zn–O(2)
O(3)–Zn–O(2)
89.78(9)
95.93(9)
95.36(9)
116.21(9)
96.51(1)
145.5(1)
111.72(9)
141.0(1)
59.81(9)
97.3(1)
258 (35000), 314 (29000)
261 (17000), 312 (18000), 345 (12000)
261 (17000), 311 (18000), 342 (13000)
261 (32000), 312 (33000), 336 (38000)
[Zn(tpda)(CF3SO3)2]
Table 4 The emission data and quantum yields (φ) for complexes 1–4
Complex 1b
Emission λ/nm
Zn–N(1)
Zn–Cl(1)
Zn–N(3)
Zn–Cl(2)
2.023(2)
2.2029(9)
2.023(2)
2.243(1)
N(1)–Zn–N(3)
N(1)–Zn–Cl(2)
N(3)–Zn–Cl(2)
N(1)–Zn–Cl(1)
N(3)–Zn–Cl(1)
93.08(9)
111.79(7)
107.56(8)
113.36(7)
116.26(8)
MeOH–
Degassed EtOH
Solid
statea
Complex
MeOHa
(1:2)b
φ
[Zn(dpa)(OAc)2]
[Zn(dpa)Cl2]
[Zn(dpa)(CN)2]
[Zn(dpa)(4-MeC6H4S)2]
[Zn(dpa)2][CF3SO3]2
[Zn(tpda)(OAc)2]
[Zn(tpda)Cl2]
359
360
359
354
360
394
392
390
349, 389
348, 390
351, 392
342, 393
352, 392
390, 418
387, 447
388, 450
378
378
363, 418
481
373
411
403
398
0.12
0.12
0.08
0.01
0.12
0.14
0.14
0.15
Complex 1d
Zn–N(1)
Zn–S(1)
Zn–N(3)
Zn–S(2)
2.051(2)
2.2761(8)
2.074(2)
2.2764(8)
N(1)–Zn–N(3)
N(1)–Zn–S(2)
N(1)–Zn–S(1)
S(1)–Zn–S(2)
89.18(8)
106.19(7)
114.08(6)
119.52(3)
Complex 2
[Zn(tpda)(CF3SO3)2]
a At 298 K. b At 77 K.
Zn–N(1)
Zn–N(3)
1.972(3)
2.001(3)
N(1)–Zn–N(1*)
N(1)–Zn–N(3)
110.8(2)
95.8(1)
The emission spectral data and quantum yields (φ) are
summarized in Table 4. For the complexes 1a–1d and 2 the
Complex 3a
Zn–N(1)
Zn–N(5)
Zn–O(3)
Zn–N(3)
Zn–O(1)
2.083(2)
2.104(2)
2.144(2)
2.129(2)
2.052(2)
N(1)–Zn–N(3)
N(1)–Zn–O(1)
N(3)–Zn–N(5)
N(3)–Zn–O(3)
N(5)–Zn–O(3)
N(1)–Zn–N(5)
N(1)–Zn–O(3)
N(3)–Zn–O(1)
N(5)–Zn–O(1)
92.14(9)
93.73(9)
90.37(9)
136.36(9)
89.04(9)
177.00(9)
88.01(9)
121.73(9)
86.34(9)
emission energies in MeOH at 298 K are the same (λmax
=
359 nm), albeit they contain different auxiliary ligands. The
emission is assigned to intraligand fluorescence since a similar
emission (λmax = 357 nm) has also been observed for free dpa.
Similarly, the emission of complexes 3a, 3b and 4 in MeOH
at 298 K (λmax = 390 nm) is dominated by the intraligand
fluorescence of the tpda ligand. The lifetimes of the fluores-
cence of these complexes are <10 ns.
In glassy solution (MeOH–EtOH 1:2 at 77 K) both intra-
ligand fluorescence and 3(π–π*) phosphorescence have been
observed. The low energy emission of all the complexes, except
3b and 4, is vibronically structured (ca. 1300 cmϪ1) with the
vibrational progression similar to the skeletal vibrational
frequency of the “free” ligand.
Complex 3b
Zn–N(1)
Zn–Cl(1)
Zn–N(2)
2.099(2)
2.3397(6)
2.126(2)
N(1)–Zn–N(2)
Cl(1)–Zn–Cl(1*)
N(1)–Zn–Cl(1)
N(2)–Zn–N(2*)
N(2)–Zn–Cl(1)
N(2)–Zn–Cl(1*)
88.49(5)
124.18(3)
117.91(2)
176.98(9)
92.84(5)
88.57(5)
In the solid state the Zn–dpa derivatives, except 1d, show an
emission ranging from 363 to 378 nm which arises from the
1ππ* intraligand excited state. For 1d which shows π–π aromatic
stacking interactions in its solid state, a distinct excimeric
emission with λmax = 481 nm was observed. For the complexes
with tpda the solid state emission (λmax in 398–403 nm range) is
due to the intraligand excited states.
In this case no intermolecular hydrogen bonding interactions
between the free amino group and the sulfur atoms were
observed.
All the above complexes display supramolecular structures
in the solid state either by intermolecular hydrogen bonding
or aromatic π–π interactions. As reported previously, the
molecules of [Zn(dpa)(CN)2] 1c are bound within an infinite
two-dimensional supramolecular structure by co-operation of
both interactions.5c
However, the dichlorozinc() complexes 1b and 3b do not
display a supramolecular structure in their crystal lattices.
Their N ؒ ؒ ؒ Cl distances (3.28–3.43 Å) are too long to account
for any intermolecular hydrogen bonds, and the shortest
intermolecular separations [4.2 (1b); 4.7 Å (3b)] between two
adjacent [Zn(dpa)] moieties are too large to permit aromatic
π–π interactions.
The spectroscopic data are listed in Table 3. Complexes with
dpa, i.e. 1a–1d and 2, feature two intense absorptions at 257
and 315 nm which are assigned to intraligand π–π* transitions.
For 3a, 3b and 4 bearing the tpda ligand, the absorptions
with λmax < 345 nm (εmax > 104 dm3 molϪ1 cmϪ1) are similarly
assigned to intraligand π–π* transitions.
Conclusion
A series of blue photoluminescent zinc() complexes with di-2-
pyridylamine and 2,6-bis(2-pyridylamino)pyridine have been
prepared. Intermolecular hydrogen bonding and aromatic π–π
stacking interactions have been observed in the crystal lattice
of the complexes, and these interactions generated several types
of supramolecular structures.
Acknowledgements
We acknowledge the support from The University of Hong
Kong and The Hong Kong Research Grants Council.
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